IgE/mast cell-mediated food allergies are serious and life-threatening immediate hypersensitivity reactions. Despite being highly prevalent and clinically important, there is a limited understanding of the molecular basis of oral antigen sensitization and susceptibility to food allergies. Recently, there has been significant interest in the role of impaired intestinal barrier function in the pathogenesis of a variety of Gl disorders, including food allergies and inflammatory bowel diseases. Mast cells are key mediators in immediate hypersensitivity reactions and critical regulators of intestinal permeability. In preliminary studies, we have demonstrated an association between increased mast cells, mast cell chymase (murine mast cell protease-4 (mMCP-4)) and activated matrix metalloprotease-9 (MMP-9) with increased intestinal permeability. The central hypothesis of this proposal is that mast cell-dependent intestinal permeability is mediated by mMCP- 4-dependent activation of MMP-9. We will test this hypothesis and accomplish the objectives of this grant application by pursuing the following specific aims: Aim #1: To determine the effect of mMCP-4 on intestinal permeability;and Aim #2: To delineate the role of mMCP-4-activated MMP-9 in intestinal permeability. We will utilize in vitro, ex vivo and in vivo methods to examine the role of mMCP-4 and MMP-9 in intestinal permeability changes (transepithelial resistance and paracellular and transcellular marker flux). We will perform gelatin zymography to examine the role of mMCP-4 in intestinal MMP-9 activation. Furthermore, we will utilize novel transgenic and gene knockout mice, a murine model of oral antigen-induced food allergy and bone marrow transfer experiments to delineate the role of mast cell-derived mMCP-4 in the activation of MMP-9 and regulation of intestinal permeability. Identification of a role for mast cells, mMCP-4 and MMP-9 in intestinal permeability will have a significant impact on our understanding of the mechanisms regulating intestinal permeability in health and disease, and implications for the development of therapeutic strategies for the prevention and treatment of food allergies and possibly other gastrointestinal diseases. Relevance: This grant application will investigate the mechanisms regulating intestinal permeability, in particular the role of a protease secreted by mast cells. Understanding the regulatory mechanisms of intestinal permeability in both health and disease is required for effective treatment and prevention of food allergies and other gastrointestinal diseases.